The present invention relates to a peripheral rewinding machine and a related rewinding method for the production of rolls or logs of web material, such as paper and the like, on a tubular support or core.
In a peripheral or surface rewinding machine of the type to which the invention refers, the roll is wound around a tubular core which is set in rotation between a group of three rollers that act on the periphery of the roll being formed, and the speeds of which are kept constant and equal during the winding cycle.
The group of three motorized rollers forms a space of variable size so that the three rollers are always in contact with the roll being formed, as the roll increases in diameter. Two of the three rollers are placed at a fixed distance, so as to define a gap, through which the core is inserted, and in which the web material travels, whilst the third roller or pressure roller is movable to allow the diameter of the roll to increase and the roll to be expelled at the end of winding.
In these rewinding machines the so-called changeover stage, sometimes called cutoff and transfer, is important. That stage includes insertion of a new core in the winding space, accompanied by a special inserter, and discharge of the completed log, following severing of the web material. This severing is obtained in various ways according to the prior art, generally requiring sudden changes in the speed of two of the three winding rollers.
According to some known methods, the speed change of said rollers alone, which is naturally of rather a large magnitude, causes tensioning and tearing of the web of paper following nipping thereof against the roller along which it is fed, nipping which can take place by means of a new core which is inserted in the winding space. After severing of the web of paper, entry of the new core into the winding space and discharge of the formed log take place through differences in speed between the two input rollers and the two output rollers, respectively.
As stated previously, this method of severing the paper requires large variations in speed between the rollers, and in particular strong accelerations of the pressure roller, which cause stress on the structure of the machine. Moreover, such methods make it difficult to sever the web material along a single pre-selected perforated line to provide the completed log with exact sheet count.
Other systems use true cutting blades that cut the web at the end of winding and require complicated actuating mechanisms. Moreover, they are not very flexible in that they are tied to carrying out the cut on well-defined lengths of web material.
The object of the invention is to eliminate the drawbacks of the solutions of the prior art, and therefore to provide a rewinding machine and a rewinding method that are reliable and simple to create and ensure precise cutting of the web material.
This object is achieved with the rewinding machine and method according to the appended independent claims. Preferred embodiments of the invention are apparent from the dependent claims.
Substantially, according to the invention, a blade is carried by a rotating member which is pivoted on the axis of the roller around which the web material is wound and rotates in the same direction as the roller is provided. The rotating member is actuated when the log is in the completion stage at a speed equal to or substantially similar to that of the web material, to be subsequently slowed or accelerated when it is inside the winding space, to cause tensioning and severing of the web material. Normally severing of the material takes place along a line of perforation in the web.
Further characteristics of the invention will be made clearer by the detailed description that follows, referring to a purely exemplary and therefore non-limiting embodiment.